System and method for improving a workpiece

ABSTRACT

A method of modifying a workpiece includes providing a workpiece, determining a load stress profile associated with a load condition, the load stress profile comprising a load stress greater than a material stress limit of the workpiece, determining a residual stress profile, the residual stress profile comprising a residual stress less than the material stress limit of the workpiece, and providing the workpiece with the residual stress profile, wherein a sum of the load stress and the residual stress is less than the material stress limit of the workpiece.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Agreement No.W911W6-10-2-0007 for Future Advanced Rotorcraft Drive System (FARDS).The Government has certain rights in the invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Workpieces, such as, but not limited to, gears, may be exposed to loadsthat exceed material limits of the workpieces. In some cases, repeatedor cyclic exposure to loads may lead to fatigue failure of a workpiece,especially when a workpiece is exposed to loads of vastly differentdirectional components.

SUMMARY

In some embodiments of the disclosure, a method of modifying a workpieceis disclosed as comprising providing a workpiece, determining a loadstress profile associated with a load condition, the load stress profilecomprising a load stress greater than a material stress limit of theworkpiece, determining a residual stress profile, the residual stressprofile comprising a residual stress less than the material stress limitof the workpiece, and providing the workpiece with the residual stressprofile, wherein a sum of the load stress and the residual stress isless than the material stress limit of the workpiece.

In other embodiments of the disclosure, an apparatus is disclosed ascomprising processor configured to determine a tensile limit curve ofthe workpiece as a function of a dimension of the workpiece, determine acompressive limit curve of the workpiece as a function of the dimensionof the workpiece, determine a tensile load stress profile associatedwith a tensile load condition, the tensile load stress profilecomprising a tensile load stress curve as a function of the dimension ofthe workpiece, determine a compressive load stress profile associatedwith a compressive load condition, the compressive load stress profilecomprising a compressive load stress curve as a function of thedimension of the workpiece, and determine a residual stress profile, theresidual stress profile comprising a residual stress curve as a functionof the dimension of the workpiece, wherein a summation of the residualstress curve and the tensile load stress curve is less than the tensilelimit curve of the workpiece along the dimension, and wherein asummation of the residual stress curve and the compressive load stresscurve is greater than the compressive limit curve along the dimension.

In yet other embodiments of the disclosure, an apparatus is disclosed ascomprising a processor and a memory coupled to the processor, whereinthe memory comprises instructions that cause the processor to determinea first contact stress associated with a mesh point of a tooth of agear, determine a first bending stress associated with a root of thetooth, determine a first residual stress to the gear as a function ofthe first contact stress, and provide a second residual stress as afunction of the first bending stress.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and theadvantages thereof, reference is now made to the following briefdescription, taken in connection with the accompanying drawings anddetailed description:

FIG. 1 is a flowchart of a method of improving a workpiece according toan embodiment of the disclosure;

FIG. 2 is a partial view of a workpiece according to an embodiment ofthe disclosure; and

FIG. 3 is a workpiece optimization chart according to an embodiment ofthe disclosure.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

In some cases, it may be desirable to improve a workpiece, such as, butnot limited to, a load bearing component, by making the workpiece moreresistant to failure as a result of deformation, internal restructuring,and/or fatigue. In some embodiments of the disclosure, systems andmethods are disclosed that comprise determining a stress or stressprofile that a workpiece may experience when exposed to a load or loadprofile and thereafter providing the workpiece with a residual stress orresidual stress profile as a function of the stress or the stressprofile so that the workpiece service life and/or strength may beimproved.

Referring now to FIGS. 1-3, a method 100 of improving a workpiece, agear 200 (a subject workpiece of the method 100), and a workpieceoptimization chart 300 (showing the findings of various steps of themethod 100) are shown, respectively. Most generally, the method 100 maybe implemented to improve a workpiece, such as the gear 200 of FIG. 2,to improve the service life or strength of the gear 200 in accordancewith the curves of FIG. 3 as described below.

The method 100 may begin at block 102 by determining workpiece tensilelimits. Most generally, the term tensile may refer to workpiece strengthlimits as a load is generally applied to the workpiece in a firstdirection. In some embodiments, the workpiece tensile limits may bedetermined as a function of the material composition of the workpiece,the structure and/or shape of the workpiece, a working temperature of anenvironment in which the workpiece is anticipated to be utilized, aworking temperature of the workpiece, and any already applied materialtreatment processes applied to the workpiece. In some cases, theworkpiece tensile limits may be obtained from a manufacturer providedspecification of the workpiece. In other cases, the tensile limits maybe experimentally obtained through laboratory testing of a substantiallyidentical workpiece. Regardless the method of obtaining the tensilelimits of the workpiece, in some embodiments the workpiece tensilelimits may be represented as a plot or curve of the maximum principalstress (as measured in pressure per square inch (psi) versus a dimensionof the workpiece. In some cases, the tensile limit values may be plottedversus a depth below an outer surface of a tooth root 202 of the gear200. As shown in FIG. 3, the workpiece tensile limit curve 302 isrelatively flat with only a slight decrease in strength as measureddeeper from the surface of the tooth root 202. Most generally, the depthmay be considered to be measured in a direction parallel to a directionnormal to the surface of a portion of the tooth root 202. However,because the tooth root 202 comprises a plurality of surface points fromwhich a depth may be measured, it will be appreciated that the workpieceoptimization chart 300 is directed mostly to a selected surface point204 of the tooth root 202 and that workpiece optimization chartsassociated with other surface points of the tooth root 202 may yielddifferent curves.

The method 100 may continue at block 104 by determining workpiececompressive limits. Most generally, the term compressive may refer toworkpiece strength limits as a load is generally applied in a seconddirection that is generally opposed and/or opposite to the firstdirection. In some embodiments, the workpiece compressive limits may bedetermined as a function of the material composition of the workpiece,the structure and/or shape of the workpiece, a working temperature of anenvironment in which the workpiece is anticipated to be utilized, aworking temperature of the workpiece, and any already applied materialtreatment processes applied to the workpiece. In some cases, theworkpiece compressive limits may be obtained from a manufacturerprovided specification of the workpiece. In other cases, the compressivelimits may be experimentally obtained through laboratory testing of asubstantially identical workpiece. Regardless of the method of obtainingthe compressive limits of the workpiece, in some embodiments theworkpiece compressive limits may be represented as a plot or curve ofthe maximum principal stress (as measured in psi) versus a dimension ofthe workpiece. In some cases, the compressive limit values may beplotted versus a depth below an outer surface of a tooth root 202 of thegear 200. As shown in FIG. 3, the workpiece compressive limit curve 304may increase in strength as measured deeper from the surface of the root202. It will be appreciated that while the workpiece tensile limits aredenoted as positive pressure values, the workpiece compressive limitvalues are denoted as negative pressure values as a function of theopposite directional forces associated with the limits. The workpiececompressive limit curve 304 is measured relative to the selected surfacepoint 204 of the tooth root 202 in a manner similar to that of theworkpiece tensile limit curve 302. In some cases, the workpiece tensilelimit curve 302 should not be exceeded by forces greater than theworkpiece tensile limit curve 302 or the workpiece may deform.Similarly, the workpiece compressive limit curve 304 should not beexceeded by forces greater (or higher negative value as shown onworkpiece optimization chart 300) or the workpiece may deform.Accordingly, the workpiece tensile limit curve 302 and the workpiececompressive limit curve 304 may bound or envelope operational values offorces or loads that the workpiece or gear 200 may withstand withoutdeformation along the tooth root 202 as measured along a depthassociated with the selected surface point 204.

The method 100 may continue at block 106 by determining a tensile loadstress profile of the workpiece. More specifically, a known oranticipated load or combination of loads may be experimentally appliedto the workpiece and/or applied to the workpiece through modeling viafinite element analysis (whether computerized or otherwise) to determinea tensile load stress profile for the workpiece under the tensile loadconditions. In some embodiments, the workpiece tensile load stressprofile may be determined as a function of the material composition ofthe workpiece, the structure and/or shape of the workpiece, a workingtemperature of an environment in which the workpiece is anticipated tobe utilized, a working temperature of the workpiece, and any alreadyapplied material treatment processes applied to the workpiece. In somecases, the workpiece tensile load stress profile may be obtained from amanufacturer provided specification of the workpiece. In other cases,the workpiece tensile load stress profile may be experimentally obtainedthrough laboratory testing of a substantially identical workpiece.Regardless of the method of obtaining the workpiece tensile load stressprofile of the workpiece, in some embodiments the workpiece tensile loadstress profile may be represented as a plot or curve of the maximumprincipal stress (as measured in psi) versus a dimension of theworkpiece. In some cases, the workpiece tensile load stress profile maybe plotted versus a depth below the outer surface of the tooth root 202of the gear 200. As shown in FIG. 3, the workpiece tensile load stresscurve 306 may exceed the workpiece tensile limit curve 302 near thesurface and decrease in strength as measured deeper from the surface ofthe tooth root 202. The workpiece tensile load stress curve 306 ismeasured relative to the selected surface point 204 of the tooth root202 in a manner similar to that of the workpiece tensile limit curve302. Because portions of the workpiece tensile load stress curve 306 aregreater than the respective (based on depth) workpiece tensile limitcurve 302 values, the workpiece optimization chart 300 may indicate thatthe workpiece may fail to handle the applied tensile load conditionswithout deformation. Accordingly, there may be an opportunity to improvethe workpiece through the use of a variety of treatment processes toallow the workpiece to withstand the application of the tensile loadconditions after the application of the treatment processes. Thetreatment process may comprise shot peening, carburizing, cavitationpeening, laser peening, heat treatments, low plasticity burnishing,quenching, and/or any other suitable method of altering strength of theworkpiece or gear 200, particularly at the surface of the workpiece orgear 200.

The method 100 may continue at block 108 by determining a compressiveload stress profile of the workpiece. More specifically, a known oranticipated load or combination of loads may be experimentally appliedto the workpiece and/or applied to the workpiece through modeling viafinite element analysis (whether computerized or otherwise) to determinea compressive load stress profile for the workpiece under thecompressive load conditions. In some embodiments, the workpiececompressive load stress profile may be determined as a function of thematerial composition of the workpiece, the structure and/or shape of theworkpiece, a working temperature of an environment in which theworkpiece is anticipated to be utilized, a working temperature of theworkpiece, and any already applied material treatment processes appliedto the workpiece. In some cases, the workpiece compressive load stressprofile may be obtained from a manufacturer provided specification ofthe workpiece. In other cases, the workpiece compressive load stressprofile may be experimentally obtained through laboratory testing of asubstantially identical workpiece. Regardless of the method of obtainingthe workpiece compressive load stress profile of the workpiece, in someembodiments the workpiece compressive load stress profile may berepresented as a plot or curve of the maximum principal stress (asmeasured in psi) versus a dimension of the workpiece. In some cases, theworkpiece compressive load stress profile may be plotted versus a depthbelow the outer surface of the tooth root 202 of the gear 200. As shownin FIG. 3, the workpiece compressive load stress curve 308 may notexceed the workpiece compressive limit curve 304. The workpiececompressive load stress curve 308 is measured relative to the selectedsurface point 204 of the tooth root 202 in a manner similar to that ofthe workpiece tensile limit curve 302. Because the workpiece compressiveload stress curve 306 does not exceed (with greater negative values) theworkpiece compressive limit curve 304 values, the workpiece optimizationchart 300 may be referred to as indicating that the workpiece may handlethe applied compressive load conditions without deformation.

The method 100 may continue at block 110 by determining a residualstress profile or residual stress curve 310 that when added to theworkpiece tensile load stress curve 306, yields a resultant tensilestress curve 312 that does not exceed the workpiece tensile limit curve302. In some embodiments, a residual stress curve 310 may be selected toproduce a resultant tensile stress curve 312 that comprises a safestrength margin or offset between the resultant tensile stress curve 312and the workpiece tensile load stress curve 306. In such cases, when theworkpiece or gear 200 is provided with a residual stress curve 310 thatsuitably enables accommodation of the tensile load conditions describedabove, the workpiece will not deform in response to the application ofthe tensile load condition. However, the residual stress curve 310 mustalso be selected so that when a compressive load condition (such issometimes the case in a gear 200 experiencing cyclical loading and/ordirectional changes in loading), a resultant compressive stress curve314, defined as the summation of the residual stress curve 310 and theworkpiece compressive load stress curve 308, does not exceed theworkpiece compressive limit curve 304. If the compressive stress curve314 exceeds the workpiece compressive limit curve 304, the workpiece maydeform, or in the least, internally reconfigure to alter any previouslyprovided residual stress designed to accommodate and/or offset thetensile load conditions.

The method 100 may progress to block 112 where the determined residualstress curve 310 is imparted to or provided to the workpiece or gear200. In some embodiments, the residual stress curve 310 may be providedto the workpiece or gear 200 through any of the above-describedworkpiece treatment methods. However, in some embodiments, cavitationpeening, laser peening, and/or low plasticity burnishing may be utilizedwhere greater control or an ability to apply such treatments to only arelatively small selected portion of a workpiece or gear 200 is desired.

Referring now to FIG. 2, in some cases, the method 100 may be repeatedin whole and/or in part for a single workpiece or gear 200 to beimparted with a plurality of different residual stress profiles. Notonly can residual stress profiles be provided to the selected surfacepoint 204 of tooth root 202, but other residual stress profiles may beapplied at a second surface point 206 of tooth root 202 or at one ormore mesh points 208 of gear 200. In other words, while the method 100may generate a workpiece optimization chart 300 specific to a selectedsurface point, the method 100 may be generalized and applied at anysurface point of a workpiece or gear 200. In some cases, the method 100may first be applied to the gear 200 so that a workpiece tensile loadstress curve 306 may be associated with a contact stress associated withthe mesh point 208 of the gear 200 and the method 100 may secondly beapplied to the gear 200 so that the workpiece tensile load stress curve306 may be associated with a bending stress associated with the toothroot 202 of the gear 200. Accordingly, a gear 200 may be provided atleast two different residual stress profiles tailored to the loadingconditions of different features of the gear 200.

Still further, while method 100 is described as generating residualstress profiles as a function of depth of a workpiece, in alternativeembodiments, the method 100 may be generalized and configured to provideresidual stress profiles as a function of a variation in surfacelocation along a predetermined translational path of the workpiece, suchas a path along an external surface of the workpiece. For example, apredetermined external surface path of the workpiece may be defined andthe residual stress profile may be provided as a function of thepredetermined external surface path with the depth along thepredetermined external surface path being a constant. Alternatively, insome embodiments, a two or three dimensional matrix, a spreadsheet, acomputer model, and/or any other suitable manner of accommodatingcomplex multidimensional data sets may be utilized so that a residualstress profile is not restricted to being applied to a particularselected location of a workpiece or gear 200. Rather, the residualstress profile may represent a complete or partial solution for a threedimensional space of the workpiece or gear 200. Accordingly, bygeneralizing the method 100, a particular workpiece may be evaluated foruse in a predetermined set of loading conditions and thereafter may betreated so that, as a function of determining a residual stress solutionfor the workpiece (potentially as a whole) and providing the workpiecewith the residual stress profile, the workpiece is optimized forexposure to the predetermined set of loading conditions and the life ofthe workpiece may be lengthened.

At least one embodiment is disclosed and variations, combinations,and/or modifications of the embodiment(s) and/or features of theembodiment(s) made by a person having ordinary skill in the art arewithin the scope of the disclosure. Alternative embodiments that resultfrom combining, integrating, and/or omitting features of theembodiment(s) are also within the scope of the disclosure. Wherenumerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example,whenever a numerical range with a lower limit, R_(l), and an upperlimit, R_(u), is disclosed, any number falling within the range isspecifically disclosed. In particular, the following numbers within therange are specifically disclosed: R=R_(l)+k*(R_(u)−R_(l)), wherein k isa variable ranging from 1 percent to 100 percent with a 1 percentincrement, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5percent, . . . , 50 percent, 51 percent, 52 percent, . . . , 95 percent,96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Unlessotherwise stated, the term “about” shall mean plus or minus 10 percentof the subsequent value. Moreover, any numerical range defined by two Rnumbers as defined in the above is also specifically disclosed. Use ofthe term “optionally” with respect to any element of a claim means thatthe element is required, or alternatively, the element is not required,both alternatives being within the scope of the claim. Use of broaderterms such as comprises, includes, and having should be understood toprovide support for narrower terms such as consisting of, consistingessentially of, and comprised substantially of. Accordingly, the scopeof protection is not limited by the description set out above but isdefined by the claims that follow, that scope including all equivalentsof the subject matter of the claims. Each and every claim isincorporated as further disclosure into the specification and the claimsare embodiment(s) of the present invention.

What is claimed is:
 1. A method of modifying a workpiece, comprising:providing a workpiece; determining a tensile load stress profileassociated with a tensile load condition, the tensile load stressprofile comprising a tensile load stress beyond a tensile stress limitof the workpiece; determining a compressive load stress profileassociated with a compressive load condition, the compressive loadstress profile comprising a compressive load stress within a compressivestress limit of the workpiece; determining a residual stress profile,the residual stress profile comprising a residual stress within thetensile stress limit of the workpiece, wherein a sum of the tensilestress and the residual stress is within the tensile stress limit and asum of the compressive stress and the residual stress is within thecompressive stress limit of the workpiece; and providing the workpiecewith the residual stress profile.
 2. The method of claim 1, wherein thesum of the compressive stress and the residual stress is more positivethan a compressive stress limit of the workpiece.
 3. The method of claim1, wherein the load condition is a cyclic load condition.
 4. The methodof claim 1, wherein the workpiece is a gear.
 5. The method of claim 1,wherein the providing the workpiece with the residual stress profilecomprises cavitation peening.
 6. The method of claim 1, wherein theproviding the workpiece with the residual stress profile comprises laserpeening.
 7. The method of claim 1, wherein the determining thecompressive load stress profile or determining the tensile load stressprofile comprises a finite element analysis of the workpiece.
 8. Themethod of claim 1, wherein at least one of the compressive load stressprofile and the residual stress profile are determined as a function ofa depth of the workpiece.
 9. The method of claim 1, wherein at least oneof the compressive load stress profile and the residual stress profileare determined as a function of an outer profile translation path of theworkpiece.
 10. An apparatus comprising: a processor configured to:determine a tensile limit curve of the workpiece as a function of adimension of the workpiece; determine a compressive limit curve of theworkpiece as a function of the dimension of the workpiece; determine atensile load stress profile associated with a tensile load condition,the tensile load stress profile comprising a tensile load stress curveas a function of the dimension of the workpiece; determine a compressiveload stress profile associated with a compressive load condition, thecompressive load stress profile comprising a compressive load stresscurve as a function of the dimension of the workpiece; and determine aresidual stress profile, the residual stress profile comprising aresidual stress curve as a function of the dimension of the workpiece;wherein a summation of the residual stress curve and the tensile loadstress curve is less than the tensile limit curve of the workpiece alongthe dimension; and wherein a summation of the residual stress curve andthe compressive load stress curve is greater than the compressive limitcurve along the dimension.
 11. The apparatus of claim 10, wherein adirection of the first load condition is different than a direction ofthe second load condition.
 12. The apparatus of claim 10, wherein thedimension is a depth of the workpiece.
 13. The apparatus of claim 10,wherein the dimension is a translational path along an outer surface ofthe workpiece.
 14. The apparatus of claim 10, wherein the workpiece is agear.
 15. The apparatus of claim 10, further configured to provide theresidual stress profile to the workpiece.
 16. An apparatus comprising: aprocessor; and a memory coupled to the processor, wherein the memorycomprises instructions that cause the processor to: determine a firstcontact stress associated with a mesh point of a tooth of a gear;determine a first bending stress associated with a root of the tooth;determine a first residual stress to the gear as a function of the firstcontact stress; and provide a second residual stress as a function ofthe first bending stress.
 17. The apparatus of claim 16, wherein a sumof the first contact stress and the first residual stress is less than afirst stress limit of the tooth and wherein a sum of the first bendingstress and the second residual stress is less than a second stress limitof the tooth.
 18. The apparatus of claim 16, wherein a sum of the firstcontact stress limit and the first residual stress is greater than afirst compressive yield limit of the tooth and wherein a sum of thefirst bending stress and the second residual stress is greater than asecond compressive yield limit of the tooth.
 19. The apparatus of claim16, wherein at least one of the providing the first residual stress andproviding the second residual stress comprises at least one of laserpeening, cavitation peening, and low plasticity burnishing.
 20. Theapparatus of claim 16, wherein the first contact stress and the firstresidual stress are associated with a first depth associated with themesh point and wherein the second contact stress and the second residualstress are associated with a first depth associated with the root.